1. Field of the Invention
The invention generally relates to an evaporative fuel control system having a fill-up control valve disposed in a vent line that communicates a fuel tank with a canister, and in particular to such an evaporative fuel control system in which the fill-up control valve is located outside and above the fuel tank so that fuel does not spill out of the top of a filler pipe during refueling immediately after the fuel tank is filled up.
2. Description of Related Art
An automobile, or the like, is provided with a fuel tank that stores fuel to be supplied to a combustion chamber of an engine. The fuel tank is provided with a vent system that allows air to enter or leave the fuel tank in accordance with a reduction or increase in the quantity of fuel in the tank. The vent system communicates the interior of the fuel tank with a canister. If the fuel level in the fuel tank rises above or exceeds the full position, for example, overflowing fuel is fed to the canister, to wet the canister and make it unable to use. In view of this situation, a fill-up control valve is provided in the upper portion of the fuel tank, for shutting off the vent system and preventing air and fuel from being fed to the canister when the fuel in the fuel tank reaches the full level.
In addition to the fill-up control valve as described above, a fuel cut-off valve is also mounted in the fuel tank. The fuel cut-off valve is normally in an open position to keep the interior of the fuel tank exposed or released to the atmosphere so as to adjust variations in the pressure within the fuel tank, and is placed in a closed position when the automobile is inclined or rolls over. The fill-up control valve, fuel cut-off valve, canister and other components cooperate to form an evaporative fuel control system. Thus, the evaporative fuel control system functions to control fill-up of the fuel tank, reduce variations in the pressure in the fuel tank, and prevent discharge or emission of fuel vapors to the outside.
FIG. 7 shows an example of a fuel tank in which a conventional evaporative fuel control system is installed. As shown in FIG. 7, the fuel tank 1 installed on an automobile, or the like, stores fuel to be supplied to the engine. A fill-up control valve A and a fuel cut-off valve B are mounted in the upper portion of the fuel tank 1. The fill-up control valve A is connected to a canister 4 via a vent line 5a, and the fuel cut-off valve B is connected to the canister 4 via a vent line 5b. To the fuel tank 1 is attached a filler pipe 3 that is closed by a filler cap (not shown). Upon refueling, fuel is supplied to the fuel tank 1 as needed through the filler pipe 3 by means of a fuel supply gun 2. An example of this type of evaporative fuel control system is disclosed in Japanese Laid-open Patent Publication No. 7-151018.
FIG. 6 shows an example of the fill-up control valve A. The fill-up control valve A includes a casing 10 that is inserted in the fuel tank 1, a float 11 disposed in the casing 10, a spring 12 that urges the float 11 upward, a valve body 13 attached to the upper portion of the float 11, a vent line 5a, and so forth. The vent line 5a is connected at its one end with the downstream side of the valve body 13, and is connected at the other end with the canister 4.
The casing 10 has a hollow, cylindrical shape, and is open at its upper and lower ends. A float chamber 17 is formed in the casing 10, and a valve seat 15 is formed above the float chamber 17. Furthermore, a plurality of vertical ribs 16 are formed at equal intervals on the inner circumferential surface of the casing 10, such that the ribs 16 extend in radial directions from the casing 10 toward the float 11. The vertical ribs 16 serve to guide the float 11 during its vertical movements.
Two or more vent holes 18a are formed through the side wall of the casing 10, and a bottom plate 19 having two or more vent holes 18b is attached to the bottom of the casing 10. In operation, the fuel in the fuel tank 1 enters the float chamber 17 through the vent holes 18a, 18b. Also, a flange 14 is formed on the outer periphery of the casing 10, and the casing 10 is mounted in the fuel tank 1 such that the flange 14 is attached to the upper surface of the tank 1.
With the fill-up control valve A constructed as described above, when fuel is supplied to the fuel tank 1 through the filler pipe 3, and the fuel level in the fuel tank 1 rises and reaches the casing 10 of the fill-up control valve A after a while, the fuel enters the float chamber 17 through the vent holes 18a of the casing 10 and the vent holes 18b of the bottom plate 19. As a result, the fuel pushes up the float 11, and the valve body 13 at the upper surface of the float 11 abuts on the valve seat 15. Since the vent line 5a is closed when the valve body 13 abuts on the valve seat 15, subsequent refueling causes an increase in the pressure in an air chamber K located above the upper surface of the fuel, and the fuel level rises toward the top of the filler pipe 3. When the fuel reaches the tip of the fuel supply gun 2, refueling is automatically stopped. The fuel level reached at this time provides the full position or full level M as indicated in FIG. 6.
In the meantime, the fuel tank 1 of the automobile has been desired to be reduced in size and weight, and has also been desired to be supplied with as much fuel as possible. To this end, the full position of the fuel tank 1 must be set to a high level, resulting in a reduction in the volume of the air chamber K that is left above the upper surface of the fuel when the fuel tank 1 is filled up. In the case of refueling of the fuel tank 1 designed as described above, after the fuel is supplied up to the full position at which the fill-up control valve A is actuated, the pressure in the air chamber K rapidly increases because of the reduced volume of the air chamber K left above the upper surface of the fuel. As the pressure in the air chamber K rapidly increases, the fuel level rapidly rises toward the top of the filler pipe 3, and a part of the fuel may spill out of the top of the filler pipe 3 as shown in FIG. 7.
The fill-up control valve A has the larger size than the fuel cut-off valve B. In the conventional system as described above, the fill-up control valve A, which is mounted on the upper surface of the fuel tank 1, takes up increased space on the upper surface of the tank 1, which may place a large restriction on the location for installation of the fuel tank, in particular, in recent automobiles in which the fuel tank is installed in the remaining space.
Furthermore, the conventional fill-up control valve A and fuel cut-off valve B communicate with the canister 4 via the vent lines 5a, 5b, respectively. This arrangement may require an increased number of pipes and an increased number of assembling steps, which may increase the manufacturing cost.